ID readers are currently used to track and sort objects moving along a line (for instance by means of a conveyor) in manufacturing and logistics operations. The ID reader can be positioned over the line at an appropriate viewing angle to acquire any expected IDs on respective objects as they each move through the field of view. The focal distance of the reader with respect to the object can vary, depending on the placement of the reader with respect to the line and the size of the object. A larger object may cause IDs thereon to be located closer to the reader, while a smaller object may contain IDs that are further from the reader. In each case, the ID should appear with sufficient resolution to be properly imaged and decoded. Therefore, the field of view of a single reader, particularly in with widthwise direction (perpendicular to line motion) is often limited. Where an object and/or the line is relatively wide, the lens and sensor of a single ID reader may not have sufficient field of view in the widthwise direction to cover the entire width of the line while maintaining needed resolution for accurate imaging and decoding of IDs. Failure to image the full width can cause the reader to miss IDs that are outside of the field of view.
Several techniques can be employed to overcome the limitation in field of view of a single ID reader and expand the overall field of view in the widthwise direction. For instance, a line-scan system with inherently wider FOV can be employed; however, this arrangement increase complexity and costs as it requires more specialized hardware (an encoder is often needed to sense relative movement of the line when using a line-scan arrangement). Another technique is to employ a larger sensor in the single ID reader to provide the desired resolution for appropriately imaging the scene along the widthwise direction; however, this approach entails additional cost through the use of less-conventional hardware and an enlarged FOV resolution. The increased height direction may cause the sensor to capture the same ID in a plurality of captured image frames as the object passes through the enlarged field of view. This, in turn leads to extraneous processing and/or decoding of the same ID and the risk that a single object is mistaken for a plurality of objects passing under the reader. Another technique is disclosed in patent document EP2624042-B1, which provides a field of view expander using several mirrors.
However, when the object moving along the line is a container, and the mark to be read is a barcode printed on a cylindrical portion of the lateral wall of the container, the use of a single ID reader does not guarantee the correct identification and reading of the mark, even if the field of view of the single ID reader has been expanded. The mark may be placed on the opposite side of the lateral wall relative to the framing of the ID reader, such that the container passes thorough the reading area undetected.
To make sure that the mark printed on the cylindrical portion of the container is always read, one can employ multiple ID readers or cameras disposed around a reading area of the line such that at least one of the cameras is able to capture the mark of the container. For example, known systems require the use of four cameras to read the mark printed on a bottle or can. However, this solution presents several drawbacks. Firstly, this is an expensive and complex solution that requires additional hardware and optics (several cameras) which in some cases must be fully synchronized. Moreover, this system cannot guarantee that every container will present a full view of the mark to one of the cameras while progressing down the conveyer. For example, when the conveyor transporting the containers is wide enough to allow two or more containers passing by at the same time, the mark printed on some of these containers may be obfuscated (e.g. partially or fully covered) by the presence of other containers blocking the field of view. Besides, the special arrangement of the mark on a cylindrical wall makes it difficult to capture the full mark by one camera (i.e. in some cases the cameras only can partially capture the mark), rendering the barcode undetected, unless a specific and complex software is used to integrate the different images of the cameras to detect the mark (e.g. by stitching the different barcode fragments to generate an entire code). Furthermore, when the line is running fast (e.g. with a feeding frequency of more than 80 containers per minute), all these problems are aggravated.
Therefore, there is a need for a device and method that allows safe capture, with a success rate of 100%, of marks (such as 1D or 2D barcodes) printed on a container moving on a horizontal conveyer. Preferably, container codes must be read at a rate capable of sustaining the line feeding frequency for these kinds of containers (normally of around 60 to 120 containers per minute).